The Affordable Care Act mandates that Medicare dramatically reduce spending to help pay for federal subsidies in the new health insurance exchanges. One upshot: a massive “demonstration” to see if $248 million can be saved this year in the care of California’s oldest, disabled and poorest residents, including 200,000 in Los Angeles County.

Almost half of all individuals in the state who are eligible for both Medicare and Medi-Cal benefits are being steered to special Medi-Cal managed care plans where their health needs are supposed to be coordinated, and where federal and state payments are limited to a set fee per patient, eliminating open-ended fees for services.

It sounds good, except that lots of vulnerable people — many in nursing homes or suffering cognitive impairment — suddenly find themselves stripped of their regular doctor, and facing a bureaucratic maze to get that care reinstated.

Beginning this spring, thousands of so-called dual eligibles each month receive packets advising that they must sign up with one of the plans, or the state will sign for them. If they want to keep their current doctors — notably, many paid by Medicare on a fee-for-service basis — they must proactively say so.

Advocates for the elderly and disabled — including the National Senior Citizens Law Center, the Center for Health Care Rights, and Neighborhood Legal Services of L.A. County, as well as the county Medical Association — say thousands don’t understand what is at stake and have been unwittingly drafted into the demonstration.

Some have seen gaps open in critical services, including chemotherapy, or sight-saving eye injections or prescriptions, because their previous providers say they are no longer on their patient list. Appeals to get such situations corrected are difficult for the cognitively impaired, especially for those who have no one to speak up for them. The state will not recognize an appeal unless it comes directly from the patient, or someone registered with the state as a health surrogate.

The state Department of Health Care Services (DHCS), which manages the demonstration, says it puts a high priority on continuity of care and says that it is trying to make sure that Californians who get the enrollment packets understand their responsibilities.

DHCS says the managed care plans will assist enrollees in many ways, including added dental and transportation benefits, and improved health care and social service coordination to help people stay out of hospitals and nursing homes.

But many Medi-Cal managed care plans have a reputation for reduced numbers of doctors and hospitals and that understandably frightens many dual eligibles. As of August, the most recent data available, 20,981 Los Angeles County residents had enrolled in the demonstration, while 36,552 had opted to keep their current doctors. In California, 42,473 had enrolled and 55,511 had opted out.

Advocates were dealt a setback last week when procedural issues forced the Medicaid Defense Fund to withdraw a federal lawsuit seeking to block Medicare and Medi-Cal from further enrollments in the demonstration. A similar lawsuit in state court failed in August. The judge ruled then that the plaintiffs had not shown that patients would be harmed by the project.

A recent study by the UCLA Center for Health Policy Research pointed in another direction.

Many of the people who are likely enrollees “are so physically, mentally and socially vulnerable,” the study concluded, “that they could not withstand even temporary gaps in care.”

Roger Smith is managing editor of the California HealthCare Foundation Center for Health Reporting at USC Annenberg, which partners with news organizations in California on health care issues.